This invention relates to a structure of a hybrid thick film integrated circuit assembly formed of a common emitter type power transistor and a thick film integrated circuit for controlling the power transistor.
Hybrid thick film integrated circuit assemblies of the type referred to have been previously constructed so that the collector substrate type power transistor is disposed on that surface of a ceramic substrate having formed thereon a thick film integrated circuit for controlling the power transistor and that the ceramic substrate is attached through a layer of bonding agent to a bottom of a metallic housing which serves also as a heat sink for the transistor. In those constructions heat has been principally generated in the power transistor disposed on the ceramic substrate and then spread in the latter. Subsequently the heat has dissipated through a thermal path traced from the ceramic substrate through the layer of bonding agent and thence to the metallic housing serving also as the heat sink. This has caused an increase in thermal resistance presented by that thermal path resulting in the heat dissipation effect being insufficient. Further the thermal resistance has been dependent upon the amount and/or thickness of the bonding agent resulting in the low reliability of the completed assemblies.
Accordingly it is an object of the present invention to provide an improved hybrid thick film integrated circuit assembly including a power transistor element and a thick film integrated circuit element for controlling the power transistor element and exhibiting the good heat dissipation effect while being high in reliability.
It is another object of the present invention to provide an improved hybrid thick film integrated circuit assembly including a power transistor element, a thick film integrated circuit element for controlling the power transistor element and a metallic housing for both elements permitted to be used as a grounding terminal for the assembly.